Search Results (23)

The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlO_x and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings—polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlO_x and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlO_x and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions. Full article

In the last few years, the polymerization of monomers within the nanocavities of porous materials has been thoroughly studied and developed, allowing for the synthesis of polymers with tailored morphologies, chemical architectures and functionalities. This is thus a subject of paramount scientific and technological relevance, which, however, has not previously been analyzed from a general perspective. The present overview reports the state of the art on polymerization reactions in spatial confinement within porous materials, focusing on the use of anodized aluminum oxide (AAO) templates. It includes the description of the AAO templates used as nanoreactors. The polymerization reactions are categorized based on the polymerization mechanism. Amongst others, this includes electrochemical polymerization, free radical polymerization, step polymerization and atom transfer radical polymerization (ATRP). For each polymerization mechanism, a further subdivision is made based on the nature of the monomer used. Other aspects of “in situ” polymerization reactions in restricted AAO geometries include: conversion monitoring, kinetic studies, modeling and polymer characterization. In addition to the description of the polymerization process itself, the use of polymer materials derived from polymerization in AAO templates in nanotechnology applications, is also highlighted. Finally, the review is concluded with a general discussion outlining the challenges that remain in the field. Full article

Dense and mesoporous FePd nanowires (NWs) with 45 to 60 at.% Pd content were successfully fabricated by template- and micelle-assisted pulsed potentiostatic electrodeposition using nanoporous anodic alumina and polycarbonate templates of varying pore sizes. An FePd electrolyte was utilized for obtaining dense NWs while a block copolymer, P-123, was added to this electrolyte as the micelle-forming surfactant to produce mesoporous NWs. The structural and magnetic properties of the NWs were investigated by electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The as-prepared NWs were single phase with a face-centered cubic structure exhibiting 3.1 µm to 7.1 µm of length. Mesoporous NWs revealed a core-shell structure where the porosity was only witnessed in the internal volume of the NW while the outer surface remained non-porous. Magnetic measurements revealed that the samples displayed a soft ferromagnetic behavior that depended on the shape anisotropy and the interwire dipolar interactions. The mesoporous core and dense shell structure of the NWs were seen to be slightly affecting the magnetic properties. Moreover, mesoporous NWs performed excellently as SERS substrates for the detection of 4,4′-bipyridine, showing a low detection limit of 10⁻¹² M. The signal enhancement can be attributed to the mesoporous morphology as well as the close proximity of the embedded NWs being conducive to localized surface plasmon resonance. Full article

In this work, we report the preparation of nanostructured electrodes based on dense arrays of vertically-aligned copper (Cu) nanowires (NWs) to be subsequently covered by cadmium telluride (CdTe) thin films, with great potential to be used within “substrate”-type photovoltaic cells based on A${}^{\mathrm{I}\mathrm{I}}$-B${}^{\mathrm{V}\mathrm{I}}$ heterojunctions. In particular, the multi-step preparation protocol presented here involves an electrochemical synthesis procedure within a supported anodic aluminum oxide (AAO) nanoporous template for first generating a homogeneous array of vertically-aligned Cu NWs, which are then further embedded within a compact CdTe thin film. In a second stage, we tested three deposition methods (vacuum thermal evaporation, VTE; radio-frequency magnetron sputtering, RF-MS; and electrochemical deposition, ECD) for use in obtaining CdTe layers potentially able to consistently penetrate the previously prepared Cu NWs array. A comparative analysis was performed to critically evaluate the morphological, optical, and structural properties of the deposited CdTe films. The presented results demonstrate that under optimized processing conditions, the ECD approach could potentially allow the cost-effective fabrication of absorber layer/collecting electrode CdTe/Cu nanostructured interfaces that could improve charge collection mechanisms, which in turn could allow the fabrication of more efficient solar cells based on A${}^{\mathrm{I}\mathrm{I}}$-B${}^{\mathrm{V}\mathrm{I}}$ semiconducting compounds. Full article

Magnetic nanomaterials are of great interest due to their potential use in data storage, biotechnology, or spintronic based devices, among others. The control of magnetism at such scale entails complexing the nanostructures by tuning their composition, shape, sizes, or even several of these properties at the same time, in order to search for new phenomena or optimize their performance. An interesting pathway to affect the dynamics of the magnetization reversal in ferromagnetic nanostructures is to introduce geometrical modulations to act as nucleation or pinning centers for the magnetic domain walls. Considering the case of 3D magnetic nanowires, the modulation of the diameter across their length can produce such effect as long as the segment diameter transition is sharp enough. In this work, diameter modulated Fe₆₇Co₃₃ ferromagnetic nanowires have been grown into the prepatterned diameter modulated nanopores of anodized Al₂O₃ membranes. Their morphological and compositional characterization was carried out by electron-based microscopy, while their magnetic behavior has been measured on both the nanowire array as well as for individual bisegmented nanowires after being released from the alumina template. The magnetic hysteresis loops, together with the evaluation of First Order Reversal Curve diagrams, point out that the magnetization reversal of the bisegmented FeCo nanowires is carried out in two steps. These two stages are interpreted by micromagnetic modeling, where a shell of the wide segment reverses its magnetization first, followed by the reversal of its core together with the narrow segment of the nanowire at once. Full article

Various effects caused by surface plasmons including enhanced electromagnetic field, local heating, and excited electrons/holes can not only redistribute the electromagnetic field in the time domain and space but also redistribute the excited carriers and drive chemical reactions. In this study, firstly, an Au nanoporous array photocatalyst with the arrayed gauge was prepared by means of the anodic alumina template. Then, the formation of 4,4′-dimercaptoazobenzene (DMAB) by the surface plasmon-driven photocatalysis under 633 nm laser irradiation was investigated by means of Raman spectroscopy using aminothiophenol (PATP) as a probe molecule on gold nananoporous arrays. In addition, sodium borohydride was introduced in situ to realize the reverse photocatalytic reaction driven by the surface plasma. With the help of FDTD software, the plasma distribution characteristics on the surface of Au nanoporous arrays were simulated and analyzed. Through this practical method, it is expected to draw specific graphics, letters, and Chinese characters on the micro/nano scale, and realize the functions of graphics drawing, information encryption, reading, and erasing on the micro/nano scale. Full article

Nowadays, numerous works regarding nanowires or nanotubes are being published, studying different combinations of materials or geometries with single or multiple layers. However, works, where both nanotube and nanowires are forming complex structures, are scarcer due to the underlying difficulties that their fabrication and characterization entail. Among the specific applications for these nanostructures that can be used in sensing or high-density magnetic data storage devices, there are the fields of photonics or spintronics. To achieve further improvements in these research fields, a complete understanding of the magnetic properties exhibited by these nanostructures is needed, including their magnetization reversal processes and control of the magnetic domain walls. In order to gain a deeper insight into this topic, complex systems are being fabricated by altering their dimensions or composition. In this work, a successful process flow for the additive fabrication of core/shell nanowires arrays is developed. The core/shell nanostructures fabricated here consist of a magnetic nanowire nucleus (Fe₅₆Co₄₄), grown by electrodeposition and coated by a non-magnetic SiO₂ layer coaxially surrounded by a magnetic Fe₃O₄ nanotubular coating both fabricated by means of the Atomic Layer Deposition (ALD) technique. Moreover, the magnetization reversal processes of these coaxial nanostructures and the magnetostatic interactions between the two magnetic components are investigated by means of standard magnetometry and First Order Reversal Curve methodology. From this study, a two-step magnetization reversal of the core/shell bimagnetic nanostructure is inferred, which is also corroborated by the hysteresis loops of individual core/shell nanostructures measured by Kerr effect-based magnetometer. Full article

The method of realizing nanostructures using porous alumina templates has attracted interest due to the precise geometry and cheap cost of nanofabrication. In this work, nanoporous alumina membranes were utilized to realize a forest of nanowires, providing a bottom-up nanofabrication method suitable for surface-enhanced Raman spectroscopy (SERS). Gold and iron were electroplated through the straight channels of the membrane. The resulting nanowires are, indeed, made of an active element for plasmonic resonance and SERS as the hexagonal distribution of the nanowires and the extreme high density of the nanowires allows to excite the plasmon and detect the Raman signal. The method to reduce the distance between pores and, consequently, the distance of the nanowires after electrodeposition is optimized here. Indeed, it has been predicted that the light intensity enhancement factor is up to 10¹² when the gap is small than 10 nm. Measurements of Raman signal of thiol groups drying on the gold nanowires show that the performance of the device is improved. As the thiol group can be linked to proteins, the device has the potential of a biosensor for the detection of a few biomolecules. To assess the performance of the device and demonstrate its ability to analyze biological solutions, we used it as SERS substrates to examine solutions of IgG in low abundance ranges. The results of the test indicate that the sensor can convincingly detect biomolecules in physiologically relevant ranges. Full article

One-dimensional (1D) nanostructures, such as nanotubes, nanopores, nanodots and nanocones, are characterized by better catalytic properties than bulk material due to their large active surface area and small geometrical size. These structures can be produced by several methods of synthesis including the one- and two-step methods. In the one-step method, a crystal modifier is added to the solution in order to limit the horizontal direction of structures growing during electrodeposition. In this work, NH₄Cl was used as a crystal modifier. Another way of production of 1D nanocones is the electrodeposition of metal in porous anodic alumina oxide (AAO) templates, called the two-step method. In this case, the AAO template was obtained using a two-step anodization process. Nanocones obtained by the two-step method show smaller geometrical size. In this work, cobalt nanoconical structures were obtained from an electrolyte containing CoCl₂ and H₃BO₃. The electrocatalytic properties of materials fabricated by one-step and two-step methods were measured in 1 M NaOH and compared with bulk material electrodeposited from the same electrolyte. There were several microshell structures in the case of Co deposits obtained by the one-step method. To solve this problem, different conditions of synthesis Co cones by the one-step method were applied. The electrocatalytic activity of these samples was checked as well. Full article

The development of aluminum anodization technology features many stages. With the story stretching for almost a century, rather straightforward—from current perspective—technology, raised into an iconic nanofabrication technique. The intrinsic properties of alumina porous structures constitute the vast utility in distinct fields. Nanoporous anodic alumina can be a starting point for: Templates, photonic structures, membranes, drug delivery platforms or nanoparticles, and more. Current state of the art would not be possible without decades of consecutive findings, during which, step by step, the technique was more understood. This review aims at providing an update regarding recent discoveries—improvements in the fabrication technology, a deeper understanding of the process, and a practical application of the material—providing a narrative supported with a proper background. Full article

Fe–Pd magnetic shape-memory alloys are of major importance for microsystem applications due to their magnetically driven large reversible strains under moderate stresses. In this context, we focus on the synthesis of nanostructured Fe₇₀Pd₃₀ shape-memory alloy antidot array thin films with different layer thicknesses in the range from 20 nm to 80 nm, deposited onto nanostructured alumina membranes. A significant change in the magnetization process of nanostructured samples was detected by varying the layer thickness. The in-plane coercivity for the antidot array samples increased with decreasing layer thickness, whereas for non-patterned films the coercive field decreased. Anomalous coercivity dependence with temperature was detected for thinner antidot array samples, observing a critical temperature at which the in-plane coercivity behavior changed. A significant reduction in the Curie temperature for antidot samples with thinner layer thicknesses was observed. We attribute these effects to complex magnetization reversal processes and the three-dimensional magnetization profile induced by the nanoholes. These findings could be of major interest in the development of novel magnetic sensors and thermo-magnetic recording patterned media based on template-assisted deposition techniques. Full article

One-dimensional (1D) nanostructures, such as nanotubes, nanopores, nanodots and nanocones, are characterized by better catalytic properties than bulk materials due to their large active surface area and small geometrical size. There are several methods of synthesis for these structures, including the one- and two-step methods. In the one-step method, a crystal modifier is added to the solution in order to limit the horizontal direction of structures growing during electrodeposition. In this work, cobalt nanoconical structures were obtained from an electrolyte containing CoCl₂, H₃BO₃ and NH₄Cl as the crystal modifier. Another method of production of 1D nanocones is electrodeposition of the metal into porous anodic alumina oxide (AAO) templates. This method is called the two-step method. In this case, an AAO template was obtained using two-step anodization. Then, electrodeposition of cobalt was performed from an electrolyte containing CoSO₄ and H₃BO₃. Nanocones obtained by the two-step method show smaller geometrical size. The bulk sample was electrodeposited from the same electrolyte. The electrocatalytic properties of materials fabricated by the one-step and two-step methods were measured in 1M NaOH and compared with bulk materials. Co cones obtained by the one-step method show the worst electrocatalytic properties. The hydrogen evolution reaction started the earliest for Co nanocones electrodeposited in the templates. Full article

Chemical materials are sometimes harmful to the environment as well as humans, plants, and animals. Thus, high-performance sensor systems have become more important in the past few decades. To achieve pH scale sensing in nanosystems, we applied luminescence polymer nanowires with alumina oxide template method with electrochemical polymerization. We made polymer nanowire barcode by alternately stacking poly(3-methylthiophene) (P3MT) and poly(3,4-ethylenedioxythiophene) (PEDOT) in a nanoporous template. After polymerization, a hydrofluoric acid solvent was used to remove the template, and, for changing the pH scale, we used sodium hydroxide. We measured optical properties of each part of barcode using Raman scattering and photoluminescence and confirmed that only P3MT was changed by alkali treatment. Full article

This study demonstrates a new, robust, and accessible deposition technique of metal nanoparticle arrays (NPAs), which uses nanoporous anodic alumina (NAA) as a template for capillary force-assisted convective colloid (40, 60, and 80 nm diameter Au) assembly. The NPA density and nanoparticle size can be independently tuned by the anodization conditions and colloid synthesis protocols. This enables production of non-touching variable-density NPAs with controllable gaps in the 20–60 nm range. The NPA nearest neighbor center distance in the present study was fixed to 100 nm by the choice of anodization protocol. The obtained Au NPAs have the resonant scattering maxima in the visible spectral range, with a refractometric sensitivity, which can be tuned by the variation of the array density. The thickness of the NAA layer in an Aluminum-NAA-NPA multilayer system enables further tuning of the resonance frequency and optimization for use with specific molecules, e.g., to avoid absorption bands. Applicability of the mentioned multilayers for colorimetric refractive index (RI) sensing is demonstrated. Their use as Surface-Enhanced Raman Scattering (SERS) substrates is tested using hemoglobin as a biological probe molecule. Full article

Hybrid materials play an essential role in the development of the energy storage technologies since a multi-constituent system merges the properties of the individual components. Apart from new features and enhanced performance, such an approach quite often allows the drawbacks of single components to be diminished or reduced entirely. The goal of this paper was to prepare and characterize polymer-metal hydroxide (polypyrrole-nickel hydroxide, PPy-Ni(OH)₂) nanowire arrays demonstrating good electrochemical performance. Nanowires were fabricated by potential pulse electrodeposition of pyrrole and nickel hydroxide into nanoporous anodic alumina oxide (AAO) template. The structural features of as-obtained PPy-Ni(OH)₂ hybrid nanowires were characterized using FE-SEM and TEM analysis. Their chemical composition was confirmed by energy-dispersive x-ray spectroscopy (EDS). The presence of nickel hydroxide in the synthesized PPy-Ni(OH)₂ nanowire array was investigated by X-ray photoelectron spectroscopy (XPS). Both FE-SEM and TEM analyses confirmed that the obtained nanowires were composed of a polymer matrix with nanoparticles dispersed within. EDS and XPS techniques confirmed the presence of PPy-Ni(OH)₂ in the nanowire array obtained. Optimal working potential range (i.e., available potential window), charge propagation, and cyclic stability of the electrodes were determined with cyclic voltammetry (CV) at various scan rates. Interestingly, the electrochemical stability window for the aqueous electrolyte at PPy-Ni(OH)₂ nanowire array electrode was remarkably wider (ca. 2 times) in comparison with the non-modified PPy electrode. The capacitance values, calculated from cyclic voltammetry performed at 20 mV s⁻¹, were 25 F cm⁻² for PPy and 75 F cm⁻² for PPy-Ni(OH)₂ array electrodes. The cyclic stability of the PPy nanowire array electrode up to 100 cycles showed a capacitance fade of about 13%. Full article